1. Field of the Invention
The present invention relates to a shock absorbing type steering column assembly for preventing the body of a driver from receiving a large impact at the time of a secondary collision by displacing the steering wheel forward.
2. Description of the Prior Art
Upon an automobile collision, subsequent to a so-called primary clash in which the automobile collides with another automobile, a so-called secondary collision in which the driver collides with the steering wheel occurs. In order to minimize the impact on the driver at this secondary collision to protect the driver's life, it is conventionally arranged to use a so-called collapsible steering shaft which is entirely contracted when a strong impact is given and which has a steering wheel fixed to one end thereof, and to employ an impact absorbing type of a steering column through which said steering shaft is passed.
As a shock absorbing type steering column apparatus to be used for such purpose, there is conventionally known, for example, one disclosed in Japanese Utility Model Laid-Open No. 5-75057. This conventionally-known steering column apparatus of a shock or impact absorbing type is structured as shown in FIGS. 19 to 21 of the accompanying drawings.
Referring to FIGS. 19 to 21, a steering column 1 is structured by combining, for example, an outer column with an inner column in a telescopic manner, and when a strong force is applied along the direction of the shaft (the lateral direction in FIG. 19, and the direction perpendicular to the sheet surface in FIG. 20), the entire column is contracted. Inside such steering column 1, the steering shaft 2 is supported as only being free to rotate. A steering wheel is fixed to the rear end portion of the steering shaft 2, at the portion protruding from the opening at the rear end of the steering column 1.
A supporting bracket 3 for supporting the above-mentioned steering column 1 on the car body 30 has a pair of supporting plates 4a, 4b arranged laterally. Then, both supporting plates 4a, 4b laterally sandwich therebetween a raising/lowering bracket 5 which serves as a support bracket and is fixed by welding to the lower surface of the middle portion of said steering column 1 along the width direction (the direction perpendicular to the sheet surface in FIG. 19, and the lateral direction in FIG. 20) of this steering column 1. On both of the right and left side walls of this raising/lowering bracket 5, cut-away portions 6a, 6b are formed as being open on side of the rear end edge thereof (the right end edge in FIG. 19). Also, vertically elongated holes 7a, 7b which serve as through-holes are respectively formed in portions of said supporting plates 4a, 4b which are aligned with these cut-away portions. A tilt adjusting nut 9 is threadably engaged with the tip end of a tilt adjusting bolt 8 serving as a rod-like connecting member which is passed through from one to the other of these elongated holes 7a, 7b and cut-away portions 6a, 6b (from right to left in FIG. 20). This tilt adjusting bolt 8 is arranged to raise and lower along the elongated holes 7a, 7b but is incapable of rotating due to the engagement of a head portion 10 with a side edge of elongated hole 7b.
A gap between the tilt adjusting nut 9 and the head portion 10 can be changed by rotating the tilt adjusting nut 9 by use of an unrepresented tilt adjusting lever. Then, by changing this gap, it is possible to fix the raising/lowering bracket 5 to the supporting bracket 3 an thereby fix the steering column 1, or to release such fixation of the bracket 5 in order to adjust a vertical position of the steering column 1.
Further, on a portion which exists in the middle portion of the tilt adjusting bolt 8 and the inner side of the raising/lowering bracket 5, the rear end portion of an energy absorbing member 11 (the right end portion in FIGS. 19 and 21; the front and rear sides are defined in terms of the moving direction of the automobile) is externally fitted and supported. Then, the front end portion of this energy absorbing member 11 (the left end portion in FIGS. 19 and 21) is fixed by welding to the lower surface of the middle portion of the steering column 1. Therefore, the rear end portion of the energy absorbing member 11 is supported on the car body 30 which is not displaced even at the secondary collision, through the tilt adjusting bolt 8 and the supporting bracket 3, while the front end portion of said energy absorbing member is supported by the steering column 1 which is displaced forward at the secondary collision.
This energy absorbing member 11 is formed to be corrugated, as shown in FIG. 21, by stamping out from one metallic plate having elasticity. Also, a pair of folded-back portions 13a, 13b are laterally provided and attached to a supporting portion 12 which is provided at the rear end portion of this energy absorbing member 11, and round holes 114a, 114b for inserting said tilt bolt 8 therethrough are formed in the respective folded-back portions 13a, 13b. Further, a tongue piece 15 is formed in the front end portion of the energy absorbing member 11, and this tongue piece 15 can be fixed to the lower surface of said steering column 1 by welding.
The conventional steering column apparatus of a shock or impact absorbing type, which is constituted by inserting the energy absorbing member 11 having a configuration as mentioned above between the tilt adjusting bolt 8 and the steering column 1, as shown in FIGS. 19 and 20, is operated as follows. When an impact force for pushing said steering column 1 forward is given by the secondary collision caused by an accidental collision, the energy absorbing member 11 allows said steering column 1 to be displaced forward, while being plastically deformed to be elongated in the longitudinal direction. The impact energy which is propagated from the steering wheel to the steering column 1 is absorbed because of the plastic deformation of the energy absorbing member 11. For this reason, the impact force to be applied on the body of the driver at the time of the secondary collision is mitigated so as to protect the driver.
In the conventional structure shown in FIGS. 19 to 21, there arises no special problem in terms of protection of the driver at the time of the secondary collision. However, a manufacturing cost of the energy absorbing member 11 is increased for the reason (1) described below, and moreover, an assembling process of this energy absorbing member 11 becomes complicated for the following reasons (2) and (3).
(1) The complicated configuration of the energy absorbing member 11 brings about a high manufacturing cost of the press die. Moreover, when this energy absorbing member 11 is stamped out from a steel plate, much scrap material is left, to degrade a yield on the material. PA1 (2) It is necessary to insert at the assembling the tilt adjusting bolt 8 serving as a connecting member through the pair of cut-away portions 6a, 6b, elongated holes 7a, 7b, and round holes 114a, 114b, respectively. Because of this inserting process, a process for aligning the round holes 114a, 114b provided on the energy absorbing member 11 with said cut-away portions 6a, 6b and said elongated holes 7a, 7b becomes complicated. PA1 (3) A welding process for connecting the tongue piece 15 at the front end of the energy absorbing member 11 with the lower surface of the middle portion of the steering column 1 becomes necessary. If such a welding process is conducted when the steering column apparatus of an impact absorbing type is assembled, the assembling process becomes complicated.
Because of the cost increase of the energy absorbing member owing to the above-mentioned reason (1) and a degraded efficiency of the assembling process owing to the above-mentioned reasons (2) and (3), the entire cost of the steering column apparatus of the impact absorbing type which is disclosed in Japanese Utility Model Laid-Open No. 5-75057 is increased.
As a steering column apparatus of a shock absorbing type, apart from that mentioned above, there are ones disclosed in Japanese Utility Model Laid-Open No. 6-16851, for example, and the like. However, these steering column apparatuses have the same problems as mentioned above.